The present invention relates to ram blowout preventers and shearing and sealing rams therefor.
Prior art pipe shearing rams for shearing drill strings or drill pipe are shown, for example, in U.S. Pat. Nos. 2,919,111; 2,969,838; 3,561,526; 3,590,920; and 3,766,978. However, there has been some concern as to whether cut ends of pipe or debris resulting from shearing would hamper sealing action in these shearing rams.
U.S. Pat. Nos. 3,736,982; 3,817,326 and 3,946,806 have utilized a sealing element disposed on one of two shearing rams in the shearing plane to seal between the two rams when closed. In addition to shearing and sealing operations, it is often necessary to use these rams as "blind" rams in order to seal the bore without shearing any pipe. Concern has been expressed that the sealing element between the rams might extrude beyond the ram surface after several "blind" closures. Should a need to shear drill pipe then arise, the sealing element would be exposed to damage by the sheared drill pipe. Further, the sealing element between the blades was energized by lateral movement of elastomer. Due to frictional forces, sealing pressure on the elastomer towards the center of the sealing element was reduced from that at the outer portions.
In the structure of U.S. Pat. No. 3,736,982, a lateral sealing element between the two shearing ram surfaces was energized when a ram block of an upper ram of the two rams was contacted by the lower ram. However, if drill pipe contacted the ram block during shearing, energization of the seals occurred. Thus, the lateral sealing element could be moved into a position where it was subject to damage by the sheared drill pipe. Additionally, the lateral sealing element was limited in size to a small lateral reservoir slot in one ram, and if damage by the sheared pipe was large, insufficient elastomer might be present in the reservoir to effect a seal between the two rams.